Herwig H J
Cell Tissue Res. 1976 Apr 2;167(3):297-324. doi: 10.1007/BF00219144.
A comparative ultrastructural study has been made of the pineal organ in specimens of two closely related populations of the characid fish, Astyanaz mexicanus. The specimens of one population are living in the river, under natural light conditions. The specimens of the other population, originally described as Anoptichthys jordani, are living in a completely dark cave. In specimens of both populations the pineal organ consists of a spindle shaped end-vesicle, connected to the diencephalic roof by a slender stalk. The pineal tissue is compact and consists predominantly of glia-like supporting cells and sensory cells resembling the photoreceptor cells of the lateral vertebrate eye. Phagocytotic microglia-like cells can be found in close contact with the outer segments of the sensory cells. Nerve cells are located in the neighbourhood of neuropil formations, in which synaptic contacts are established between sensory cells and nerve cells. From these nerve cells fibers are emerging, forming the pineal tract that runs down the pineal stalk towards the diencephalon. On the basis of the ultrastructure described by other authors it is concluded that the pineal organ in specimens of the river population of Astyanax mexicanus resembles the pineal organ of other fish species. In specimens of the river population, reared under normal light-dark conditions for 3, 9 or 18 months, conspicuous morphological changes have not been detected in the presumably light-sensitive outer segments of the sensory cells or in other parts of the pineal tissue. In specimens of the cave populations, reared under identical conditions, an age-dependent, gradual regression of the regular outer segment organization of the pineal sensory cells takes place. In other parts of the pineal tissue, only small morphological changes can be observed. In specimens of the cave population, reared in constant darkness, the regression of the pineal outer segment organization begins earlier and is obvious. It is postulated that the gradual age-dependent regression of the regular organization of the outer segments in the pineal organ of cave specimens of Astyanax mexicanus is genetically determined and indicates a regressive evolution of the pineal light sensitivity. The expression of the regressive traits is dependent on the environmental light conditions.
对脂鲤科鱼类墨西哥丽脂鲤两个亲缘关系密切的种群的松果体器官进行了比较超微结构研究。其中一个种群的标本生活在河流中，处于自然光条件下。另一个种群的标本最初被描述为盲眼丽脂鲤，生活在完全黑暗的洞穴中。两个种群的标本中，松果体器官均由一个纺锤形的终泡组成，通过细长的柄与间脑顶部相连。松果体组织紧密，主要由胶质样支持细胞和类似于脊椎动物侧眼感光细胞的感觉细胞组成。吞噬性小胶质样细胞可发现与感觉细胞的外段紧密接触。神经细胞位于神经毡结构附近，感觉细胞和神经细胞之间在此建立突触联系。这些神经细胞发出纤维，形成松果体束，沿松果体柄向下延伸至间脑。根据其他作者描述的超微结构得出结论，墨西哥丽脂鲤河流种群标本中的松果体器官类似于其他鱼类的松果体器官。在正常明暗条件下饲养3、9或18个月的河流种群标本中，未在推测对光敏感的感觉细胞外段或松果体组织的其他部位检测到明显的形态变化。在相同条件下饲养的洞穴种群标本中，松果体感觉细胞规则的外段组织出现与年龄相关的逐渐退化。在松果体组织的其他部位，只能观察到微小的形态变化。在持续黑暗中饲养的洞穴种群标本中，松果体外段组织的退化开始得更早且明显。据推测，墨西哥丽脂鲤洞穴标本松果体器官外段规则组织的逐渐与年龄相关的退化是由基因决定的，表明松果体光敏感性的退化进化。退化性状的表达取决于环境光照条件。
